Hydrogel is a “Water-based colloidal able to absorb water” formed by physically or chemically crosslinking a polymer chain segment. For hydrogel, a common conventional application in the biomedical field is contact lenses. In the 1960s, Wichterle and Lim et al. prepared a HEMA (hydroxyethyl methacrylate) hydrogel with a method of crosslinking to be used as contact lenses. Hydrogel is a kind of three-dimensional polymeric net structure, and has the property of swelling or diminution with adsorption or desorption of a solvent, and this kind of property means the nature of hydrogel is between a liquid and a solid.
Currently, in industry, the main method for crosslinking hydrogel comprises dissolving the powders of the hydrogel in a large volume of aqueous phase environment, dissolving a crosslinking agent in another large volume of aqueous phase environment, mixing the two products well to perform crosslinking, and after that, performing a step of drying or concentrating.